Heretofore, a communication method available in a mobile communication is limited to a voice communication method. In such a voice communication method, there are provided line memory in a data base for controlling users' location information, so that a simultaneous communication (competition) can be regulated depending on "idle" or "busy" which the line memory indicates. In case the line memory indicates "idle", the receiver side is in a non-use state and therefore a communication is allowed. However, in case the line memory indicates "busy", the receiver side is in a used-state, therefore a communication is not allowed and busy tone is sent to the transmitter side, informing that the line is busy.
Incidentally, there is an increasing need for data communication as the recent information-oriented society develops. Specifically, there is a requirement for employing a packet communication as one method of data communication in the mobile communication.
However, it is only a simultaneous communication between voice communications which has heretofore been regulated. Accordingly, it was impossible to regulate a simultaneous communication between a voice communication and a packet communication. Also, it was impossible for the communication switching system to inform, through a communication method by which another communication is undergoing, the transmitter side about a fact that the incoming communication is regulated.